9 “From Heaven You have hurled judgment: the earth has trembled, and has rested”. She which now does trouble herself, she which now speaks, has to fear at the end and to rest. Better had she now rested, that at the end she might have rejoiced. Rested? When? “When God arose unto judgment, that He might save all the meek in heart”. Who are the meek in heart? They that on snorting horses have not mounted, but in their humility have confessed their own sins. “For the thought of a man shall confess to You, and the remnants of the thought shall celebrate solemnities to You”.
The first is the thought, the latter are the remnants of the thought. What is the first thought? That from whence we begin, that good thought whence you will begin to confess. Confession unites us to Christ. But now the confession itself, that is, the first thought, does produce in us the remnants of the thought: and those very “remnants of thought shall celebrate solemnities to You.” What is the thought which shall confess? That which condemns the former life, that whereunto that which it was is displeasing, in order that it may be that which it was not, is itself the first thought.
But because thus you ought to withdraw from sins, with the first thought after having confessed to God, that it may not escape your memory that you have been a sinner; in that you have been a sinner, thou dost celebrate solemnities to God. Furthermore it is to be understood as follows. The first thought has confession, and departure from the old life. But if you shall have forgotten from what sins you have been delivered, thou dost not render thanks to the Deliverer, and dost not celebrate solemnities to your God.
Behold the first confessing thought of Saul the Apostle, now Paul, who at first was Saul, when he heard a voice from Heaven!...He put forth the first thought of obedience: when he heard, “I am Jesus of Nazareth, whom you persecute.” “O Lord,” he says, “what do You bid me to do?” This is a thought confessing: now he is calling upon the Lord, whom he persecuted. In what manner the remnants of the thought shall celebrate solemnities, in the case of Paul you have heard, when the Apostle himself was being read: “Be thou mindful that Christ Jesus has risen from the dead, of the seed of David, after my Gospel.” What is, be thou mindful? Though effaced from your memory be the thought, whereby at first you have confessed: be the remnant of the thought in the memory....
Source: The Enarrations, or Expositions, on the Psalms (New Advent)